a. Field of the Invention
The present invention pertains generally to digital data transferred over a network in conjunction with video or audio data and more specifically to synchronization of data transferred over a network with video or audio data transferred on that network or on an independent network or channel.
b. Description of the Background
Television and audio broadcast may employ a range of broadband media including cable, satellite and high speed Internet. The term broadband refers to the capability of the media or network to carry multiple channels at one time. Video and audio programs are typically allocated a constant bandwidth such that dropouts or distorted output is not produced. A channel that provides a constant minimum bandwidth rate may be referred to as isochronous or as a constant bit rate (CBR) channel. Other services that transfer data on the network, such as Internet, have typically been asynchronous, wherein bandwidth may vary depending on network load. New standards are emerging that provide for isochronous transfer of data on a network. Such standards include voice over DSL (Digital Subscriber Line) and DOCSIS (Data Over Cable System Interface Specification) and more specifically by PacketCable that provides a method for isochronous data transfers over cable.
The advent of isochronous data transfer over broadband networks enables streaming audio and video programs other than those provided by a cable or television operator. Additionally, isochronous data transfers allow the possibility for data from one channel to be synchronized with an audio/video broadcast stream or with data from another channel. Synchronized data transfer may be employed to provide modification and enhancement of a broadcast program. For example, subtitles in a number of spoken languages, or sign language, may be added to televised programs. Such additions are outside the capabilities of captioning facilities of televisions. Additionally, synchronized data transfers may be used to add local content to advertising, such as local automobile dealer information presented in conjunction with a national automobile advertisement. Data transfers must be synchronized in some manner such that subtitles appear at the correct time or advertising message enhancements appear at the correct time. Synchronized data transfers utilized in conjunction with an audio/video stream may provide increased viewer enjoyment and may provide additional opportunities for revenue. As such, a new method is needed to control the transfer of data and the utilization of that data in synchrony with an audio/video stream or data from another channel.